An exhaust gas recirculation (EGR) system that recirculates a portion of the exhaust gas to an intake passage is known as a technique to reduce the amount of NOx contained in the exhaust gas discharged from an internal combustion engine. For example, Japanese Patent Application Laid-Open No. 2004-150319 discloses an exhaust gas recirculation system of an internal combustion engine that is provided with a low-pressure EGR passage that connects the exhaust passage downstream of the turbine of the turbocharger and the intake passage upstream of the compressor of the turbocharger and a high-pressure EGR passage that connects the exhaust passage upstream of the turbine and the intake passage downstream of the compressor. The low-pressure EGR passage and the high pressure EGR passage are switched over selectively, or used simultaneously in accordance with operating conditions of the internal combustion engine.
According to a known technology, in an internal combustion engine that is equipped with a particulate filter (which will be simply referred to as a filter, hereinafter) for trapping particulate matter contained in the exhaust gas discharged from the internal combustion engine, a processing of regenerating the ability of trapping particulate matter is performed by increasing the temperature of the filter to oxidize and remove the particulate matter deposited on the filter. (Such a processing will be hereinafter referred to as regeneration processing).
Japanese Patent Application Laid-Open No. 2002-371827 and Japanese Patent Application Laid-Open No. 2005-226519 teach to detect breakage of a filter provided in an internal combustion engine based on a difference between the pressure in the upstream of the filter and the pressure in the downstream of the filter.
Japanese Patent Application Laid-Open No. 09-088727 teaches to provide a net at some point in the intake passage, in the EGR passage or in the exhaust passage between the filter and the intercooler to thereby prevent fragments of a filter or a catalyst from entering the internal combustion engine.